When a guy/girl puts his/her arm around you and you start rubbing your heads together.

Girl 1: "So how was the movie?"
Girl 2: "Great! In the middle of the movie, he put his arm around me and we started nuggling!"
Girl 1: "Wow! That's pretty serious!Was he a good nuggler?"
Girl 2: "He was great! I've never been nuggled like that before! I think he's really into me!"